Update: "Get a First Life" creator Darren got a "Proceed and Permitted" letter (the opposite of a "cease and decist") from Linden Labs:

This is an interesting bit of follow-up news that I thought might interest you guys. I don't know if it's common for Linden to do this, but I thought it was classy.

Today I awoke from my nap to a letter (via the comments on the announcement) from Linden Labs, the creators of Second Life. 'Ah, well', I though, 'here come the lawyers'.
But no. To their enormous credit, they sent me what I can only describe as a 'proceed and permitted' (instead of 'cease and desist') letter. Here's an excerpt:

"We do not believe that reasonable people would argue as to whether the website located at http://www.getafirstlife.com/ constitutes parody – it clearly is. Linden Lab is well known among its customers and in the general business community as a company with enlightened and well-informed views regarding intellectual property rights, including the fair use doctrine, open source licensing, and other principles that support creativity and self-expression. We know parody when we see it."